Over-the-wing passenger boarding bridges for servicing aircraft doorways located above or behind the wing are known in the art (U.S. Pat. No. 6,496,996, DE 10046010, WO 0009395, U.S. Pat. No. 3,538,529, U.S. Pat. No. 3,722,017). Each prior art solution provides a tunnel section that is supported in a cantilever-like fashion by an overhead support system, such that the tunnel section is positionable over the wing of the aircraft for engaging a rear doorway that is located above or behind the wing. To this end, the tunnel section typically includes at least a telescopic portion including a cab mounted at an outboard end thereof, the cab for being aligned with the rear doorway of the aircraft. In general, the tunnel section is supported at a minimum safe height above the wing, so as to provide as nearly a horizontal walking surface as possible for passengers walking therethrough. Furthermore, often the cab engages the rear doorway of the aircraft at a height above the apron that is insufficient to allow the aircraft to move away from the terminal building in the event that the over-the-wing passenger boarding bridge loses power or suffers a mechanical failure of a main elevating mechanism. During such an event, the departure of the aircraft may be delayed indefinitely while repairs are being attempted.
The above-mentioned problem is most serious for those prior art solutions that include a massive external support structure for supporting the tunnel section over the wing of the aircraft. Examples of such systems include U.S. Pat. No. 6,496,996, WO 0009395, and U.S. Pat. No. 3,538,529. In particular, the support structure is permanently mounted to the apron surface and includes a horizontally moveable extension arm that is connected to the tunnel section via variable length mechanisms. Accordingly, vertical movement of the cab mounted at the outboard end of the tunnel section can be effected only as a result of actuation of the variable length mechanisms. If the variable length mechanisms fail, then the tunnel section can only be moved along an arcuate path in a horizontal plane. Unfortunately, the design of most modern commercial aircraft wings makes it unsafe to pivot the cab away from the aircraft without also simultaneously elevating the cab above the height of certain features of the aircraft wing.
In DE 10046010, disclosed is an over-the-wing bridge including a telescoping tunnel section that is pivotally mounted at an outboard end of a radial bridge. An overhead adjustable support system is provided including an elaborate assembly of support rods, which is disposed both above and below portions of the telescoping tunnel section and the radial bridge, for supporting the telescoping tunnel section in a height adjustable manner. The over-the-wing bridge that is disclosed in DE 10046010 suffers from many of the same limitations that were described above with reference to U.S. Pat. No. 6,496,996, WO 0009395, and U.S. Pat. No. 3,538,529. However, the shorter length of the cantilevered tunnel section combined with the generally lighter weight construction of the overhead adjustable support system would make this bridge easier to manually move out of the way in the event of mechanical failure or power loss. It is a disadvantage that the aircraft would be unacceptably delayed in departing whilst preparations are being made to manually adjust the bridge. Of course, depending upon the nature of the failure, such a manual adjustment may be deemed unsafe and it would become necessary to either repair the bridge or transfer passengers to another aircraft, when available, for departure.
In fact, the above-mentioned problem is unique to the over-the-wing passenger boarding bridges. For instance, apron drive bridges, radial bridges, and the like typically do not engage an aircraft at a point behind the wing, such that the aircraft may depart even when the boarding bridge cannot be retracted in a normal fashion. Furthermore, an apron drive bridge or a radial bridge may be towed safely away from the aircraft using a tractor or another available ground vehicle. It will be obvious to one of skill in the art that prior art teachings relating to non-over-the-wing passenger boarding bridges do not address the above-mentioned problem associated with the over-the wing passenger boarding bridges.
It would be advantageous to provide a supplemental lift system for use with an over the wing passenger boarding bridge that overcomes the above-mentioned limitations of the prior art.